To make the chocolate cream, whisk together the confectioners sugar, cocoa powder and milk in a small bowl. Set aside. In a separate bowl, beat the cream with the cream of tartar until soft. Whisk in the chocolate mixture until well blended. Cover and refrigerate.

Preheat the grill or grill pan to hot. Dust the angel food cake slices with confectioners sugar. Grill the slices for 1 minute on each side until golden and grill marks appear on the surface. Transfer to serving plates and top with chocolate cream.